A new study claims there are unanswered questions about carbon sequestration and the impact of leakage on global warming.

Carbon sequestration or carbon capture and storage (CCS) is being promoted as a way to remove growing levels of CO2 from the atmosphere.

Governments around the world are investing billions of dollars over the next decade developing carbon capture and storage systems to extract CO2 at power plants and other combustion sites and store it underground.

Shaffer says storing CO2 in the deep ocean is a bad idea because of the problems it creates for deep sea life by creating a "large dead zone". He adds deep ocean stored CO2 would return to the atmosphere relatively quickly.

Geological storage of CO2 - either underground or below the ocean floor - may be more effective, but only if leakage can be kept down to 1% or less per one thousand years.

Shaffer says any long term leakage would need to be actively countered by re-sequestration, which would need to be carried out over many thousands of years.

Cook who was involved with the IPCC study says "as long as you have the right rocks to store the carbon in, then sequestration will do what nature does anyway in keeping CO2 out of the atmosphere".

"We have the Ottway Basin Project which has been going for two years. We've injected 65 thousand tonnes there with no leakage," he says. "We compress the CO2 gas into a liquid and inject it into porous rocks below non porous strata, trapping it deep underground."

Cook says the study doesn't take into account the fact that CO2 stored underground becomes denser over time.

"It will actually sink further down rather than bubble up towards the surface," he says.

But Shaffer says society should be targeting the source of CO2 rather than relying on capture and storage.

"The dangers of carbon sequestration are real and the development of CCS should not be used as a way of justifying continued high fossil fuel emissions," he says. "We should greatly limit CO2 emissions in our time to reduce the need for massive carbon sequestration and thus reduce unwanted consequences."

Cook says under the current set of circumstances CCS will be needed.

"As long as we use fossil fuels geological sequestration will need to be part of the cycle."